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  Safety Issues

Processed Wood

Processed board or sheet materials such as plywood, strandboard, hardboard and chipboard are collectively known as panel products and are made up of wood in the form of strips, veneers, chips, strands or fibres (see Datasheet 74c).

This material can also be made up in non-sheet form such as chipboard pallet blocks particularly used as deck spacers in pallets, see figure below. Sawn wood, even when accurately machined, planed or kiln dried, is not defined as processed wood. Plywood was developed to provide large panels with a dimensional stability lacking in sawn timber with good strength properties along and across the sheet. A listing of all types of sheet and their properties is in BS 1133:Section 8:2011.

Straight well-grown logs are required for peeling the veneers for plywood manufacture. The categories usually recognised within this group that are used in packaging are:-

Particleboard pallet blocks

• Plywood sheet
• Waferboard and strandboard (OSB) sheet
• Wood chipboard or composite wood blocks, particularly used in pallets,
• Wood chipboard  sheet also known as wood particleboard sheet
• Fibre building board including hardboard and medium density fibreboard (MDF)

Wood particleboard and fibre building boards were developed to provide utility sheet materials with uniform properties. They often utilise forest thinnings, lower quality trees, sawmill waste or reclaimed waste wood. The main end use in packaging is for pallet blocks with small amounts used in printers pallets where dryness is essential. Wood-based panel products are covered by a series of EN Standards but unlike previous standards, which were largely prescriptive and based on manufacturing requirements, new ENs are based on performance requirements such as the water resistance of gluelines and limiting formaldehyde gas emission. Appropriate grades of board materials for packaging are as follows:

Plywood is made from dried sheets of wood veneer and when with a water-resistant glueline (in the UK) is historically known as WBP (water and boil proof) but more recently by the European standard term Exterior. It is suitable for most end uses but for export to Australia there is also a need for phytosanitary safeguards (see ISPM 15 web page for details). Water resistant exterior glueline plywood can be used for medium term packaging but whilst defining specification to plywood suppliers is easy, it requires considerable experience to ensure you receive this grade. The pitfalls of using interior gluelines and/or species which discolour with mould or sapstain in damp conditions are often seen in plywood packaging stored outdoors. 

Waferboard and OSB (oriented strandboard) are made in a similar manner to plywood, either with randomly placed dried wood wafers, or, dried wood wafers generally running in the same direction. The strength difference is that OSB wafers are generally alligned in a single (stronger) direction. Some end uses can be the same (see our datasheet 74c) but OSB is more controlled for adhesive as it is often substituted in non-visible building industry situations for plywood. The BS EN 300 splits OSB into 4 classes for strength and durability.

Wood chipboard also called composite when made as short blocks is heavier as a sheet material and is much less strong than plywood in bending and shear stress, but as short block material for pallets it is widely used but needs care when used in place of sawn timber (both formaldehyde emmission see our sheet 88h and can also cause weakness issues with pallets in storage racking, in that in this mode of loading it is under high shear-stress). A problem also with block material is knowing the wet strength since most packaging gets wet and some unbranded material may weaken and delaminate in wet conditions. External appearance when dry is little help and the user must be confident of wet qualities, if it goes into full perimeter (highly stressed) pallets. As sheet, wood chipboard is rarely a normal choice except where used for the paper printing trade where it can be ideal since it is normally supplied (ex-manufacture) in a very dry state of about 2 to 4% moisture content (as are composite blocks).

Fibre building board is available in Standard or Tempered (latter has moisture resistance) Grade and is used for light packing case sheathing.

New materials such as finely chipped rubber from scrap vehicle tyres have been introduced as pallet blocks but the low percentage of wood in the mix means they are not classified as timber. Such material can be nailed as easily as timber and often has good compressive strength.

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